The overall goal of this study is to obtain a quantitative understanding of the fundamental determinants of the dynamic mechanical properties of the lung parenchyma. The dynamic pressure-volume behavior of excised dog lobes will be studied during steady-state sinusoidal lung volume forcing over a broad range of oscillation frequencies. The complex dynamic elastic and complex strain rate-dependent properties and energy losses of the parenchyma will be quantified as a function of the frequency and amplitude of lung deformation, state of lung inflation, and lung volume history. We will infer from these observations the roles of the lung tissue and alveolar gas-liquid interfacial properties in determining the parenchymal dynamic properties. To assist in identifying the role of the alveolar gas-liquid interfacial properties, the effects on the parenchymal properties of altering the physical properties of the alveolar surface film will be quantified. The surface film properties will be experimentally manipulated by altering the state of film compression or dilation by subjecting the lungs to different quasistatic pressure-volume cycling histories, by altering the parenchymal temperature, and by replacing the alveolar surface film with fluorocarbon liquid films. Physical mechanisms that may be operating in the lung tissue or at the gas-liquid interface will be investigated to explain the observed dynamic properties.